Thrombocytopenia

Etiology

Pseudothrombocytopenia

General Comments: in vitro artifact due to platelet agglutination via antibodies (usually, IgG, also IgM and IgA) when the calcium content is decreased by blood collection in purple top EDTA-containing blood collection tubes

If suspected, platelet count should be determined using a blue top sodium citrate-containing tube, a green top heparin-containing tube or via a peripheral smear of fingerstick blood

Antibodies against the human platelet antigen PlA1 are detected in most individuals with PTP

Patients with PTP almost universally are either multiparous women or persons who have received transfusions previously

Severe thrombocytopenia and bleeding is typical. Initial treatment consists of administration of IVIG (1 g/kg/d for 2 days) which should be administered as soon as the diagnosis is suspected

Platelets are not indicated unless severe bleeding is present, but if they are to be administered, HLA-matched platelets are preferred

A second course or IVIG, plasma exchange, corticosteroids, or splenectomy may be used in case of refractoriness

PlA1-negative or washed blood products are preferred for subsequent transfusions

Pregnancy (see Pregnancy, [[Pregnancy]]): Gestational thrombocytopenia results from progressive expansion of the blood volume that typically occurs during pregnancy, leading to hemodilution

Cytopenias result, although production of blood cells is normal or increased

Platelet counts < 100,000/mcL, however, are observed in < 10% of pregnant women in the third trimester; decreases to < 70,000/mcL should prompt consideration of pregnancy-related ITP (see above) as well as preeclampsia or a pregnancy-related thrombotic microangiopathy

In women with type 1 Von Willebrand Disease and symptomatic hemophilia carriers in whom levels of Von Willebrand factor and factor VIII usually normalize during pregnancy, the onset of post-partum hemorrhage may be delayed

Women with a history of postpartum hemorrhage have a high risk of recurrence with subsequent pregnancies

Post-Tonsillectomy (see Tonsillectomy, [[Tonsillectomy]]): Bleeding may occur early after surgery or after approximately 7 days postoperatively (with loss of the eschar at the surgical site)

Clinical Patterns of Bleeding

Clinical Manifestations

Hemorrhagic Manifestations

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The incidence of bleeding increases as platelet counts decrease below 10,000/!L. In two recent studies, the use of smaller doses of platelet concentrates resulted in a greater number of transfusions being required. The incidence of significant bleeding was greater with lower dose transfusion in one study, and not different in the other study. Current studies are addressing the issue of prophylactic versus therapeutic transfusions in patients with platelet counts less than 10,000/μL. Alloimmunization is decreased by the use of leukocyte-reduced platelets. Post- transfusion increments in platelet count decrease as the number of units transfused increases because of the development of alloimmunization. ABO incompatibility decreases the increment in platelet count post transfusion.